An electrophotographic image forming apparatus such as a copying machine and a printer has been known conventionally. The electrophotographic image forming apparatus forms a static latent image on a surface of a toner image holder, and develops this static latent image with toner provided by a developing apparatus. Then, the electrophotograpic image forming apparatus transfers and fixes thus obtained toner image onto a recording medium such as a sheet of paper.
Some image forming apparatuses employ a developer made of a toner and a carrier. In each of such image forming apparatuses, a developer made of a toner and a carrier is agitated and circulated. As a result, particles in the developer rob each other and the developer is triboelectrically charged. The triboelectrically charged toner is attracted to a static latent image formed on the toner image holder due to static suction power of the static latent image and forms a toner image, at a developing stage. Recently, because a higher speed is required for image formation, it becomes necessary to supply developer speedily and properly. In order to sufficiently and speedily agitate and transfer developer, for example, Patent Document 1 (Japanese Unexamined Patent Publication 247481/1992 (Tokukaihei 247481), published on Sep. 3, 1992) discloses an electrophotographic developing apparatus including a partition plate with comb-shaped cuts (communicating section) which partition plate is provided between developer agitating mechanisms arranged in two lines in a developer container. The developer agitating mechanisms transfer the developer in directions opposing to each other.
However, in an arrangement disclosed in Patent Document 1, the cut is provided on the partition plate not only to an upstream side of the developer agitating mechanism farther from a developing roller but also to a downstream side of this developer agitating mechanism. This causes toner to flow into a developer agitating mechanism closer to the developing roller through the cut on the downstream side of the developer agitating mechanism farther from the developing roller, before the toner is sufficiently agitated. As a result, toner that is not sufficiently charged is supplied to the developing roller. In this way, the electrophotographic developing apparatus has a poor developer agitating performance and, thereby, a poor toner charging performance. Consequently, the toner is unevenly charged. This prevents high quality image development from being performed. Moreover, because there exist a plurality of developer circulating paths, particularly, a plurality of developer paths for supplying the developer to the developing roller, an amount of the developer supplied to the developing roller varies depending on a position. This causes a problem that image formation having even toner concentration cannot be carried out.